The embodiments described herein relate to viscosified treatment fluids comprising polyol derivatized cellulose and methods of use in subterranean operations.
Viscosified treatment fluid are often used in subterranean operations. For example in fracturing operations, viscosified treatment fluids can be used as the pad fluid that is introduced into the formation at a pressure above the fracture gradient of the formation so as to create or extend at least one fracture therein. Increasing the viscosity of the fluid allows for higher pressures and may result in greater fracture length. In another example, viscosified treatment fluids can be used to transport particles downhole (e.g., for forming gravel packs or proppant packs). The viscosity of the fluid aids in suspending the particles and allows for higher concentrations of particles in the fluid.
An example of a gel system used to viscosify a treatment fluid is guar polymer with borate ions. In this gel system, borate crosslinks between the guar polymers form rapidly and are also readily broken by shear. Together, this allows for the viscosified treatment fluid to maintain viscosity in low to no shear conditions, which mitigates particle settling. Also, in shear conditions the rapid forming and breaking of crosslinks allows for the fluid to be more pumpable (e.g., requires less energy to pump) while maintaining a viscosity that, in combination with the shear, mitigates particle settling.
While the guar/borate gel systems have advantages, the guar polymer introduces disadvantages to the system. For example, because some guar polymers (e.g., carboxymethyl hydroxypropyl guar and carboxymethyl guar) are ionic at pH 8-12 where crosslinking occurs, the gel systems are sensitive to salt concentration, thereby limiting functionality in brines and in formations with salty native fluids. In another example, guar polymers tend to leave a residue in the formation that can clog some of the formation pore space and reduce permeability. Reduced permeability can reduce the efficacy of hydrocarbon production from the formation.